1. Field of the Invention
This invention relates to an electroless copper plating solution for the production of printed boards, and more particularly to an electroless copper plating solution being free from autodecomposition and having a high deposition rate, with distinguished mechanical strength of product plating film.
2. Brief Description of the Prior Art
A copper plating solution with an autocatalytic action capable of continuously depositing copper electrolessly, that is, without using electricity, is technically well known. The copper plating solution usually comprises a water-soluble copper salt, a complexing agent for copper ions (single use of a complexing agent for cupric ions or simultaneous use of a complexing agent for cuprous ions and a complexing agent for cupric ions), a reducing agent for copper ions, and a pH-controlling agent, or further a stabilizer.
Well known, typical electroless copper plating solution includes an EDTA bath containing ethylenediamine tetraacetate (EDTA) as the complexing agent and a Rochelle salt bath containing Rochelle salt as the complexing agent.
Heretofore, (1) an increase in stability, (2) an increase in plating rate, and (3) an increase in mechanical strength of plating film have been required for these plating solutions. In the electroless copper plating, the plating rate depends mainly upon a complexing agent for cupric ions, and the mechanical strength of plating film depends mainly upon a complexing agent for cuprous ions. Thus, various compounds have been investigated. As the complexing agent for cuprous ions, cyanic compounds, nitrile compounds, nitrogen-containing heterocyclic compounds (phenanthroline and its substituted derivatives and dipyridyl and its substituted derivatives), and sulfur-containing inorganic and organic compounds are now used. As the complexing agent for cupric ions, ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminetriacetic acid, diethylenetriaminetriacetic acid, diethylenetriaminepentaacetic acid, nitriloacetic acid, iminodiacetic acid, cyclohexylenediaminetetraacetic acid, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediaminecitric acid, and tartaric acid are now used.
The increase in the stability of the electroless copper plating solution can be attained by use of a stabilizer. As the stabilizer, surfactants such as polyethyleneglycolstearylamine (U.S. Pat. No. 3,804,638), polyethylene oxide, polyethylene glycol, polyether, polyester, etc. are now used. The stabilizer absorbs a substance deteriorating the stability of the plating solution, thereby increasing the stability of the plating solution. However, the stabilizer is also liable to absorption onto the surface of plating film, disturbing deposition of copper and retarding the plating rate. Furthermore, some stabilizer is liable to undergo to decomposition during the plating, forming a blackish or brittle plating film. Thus, development of technique satisfying the plating rate, mechanical strength of plating film, and stability of plating solution at the same time has been in keen demand.